Satellite -vs- Cable TV
For simplicity, from this point forward, when we say DBS, it refers to DirecTV and Dish network as well. They both operate in the same manor. DBS stands for Direct Broadcast System. DBS is the term for sending signals directly to your home by way of a satellite.
Each DBS provider currently use 3 satellites to deliver their programming to your TV. Each satellite has 32 transponders. A single transponder is one repeater channel. It receives signals from the ground station on one frequency, and sends it back to earth on a different frequency. These transponders are digital and each one can carry the compressed bit-streams of several program channels at the same time.
Here is where DBS becomes complex.
DBS sends their digital signal to the satellite on a Ka or Ku band frequency. A transponder in the satellite receives that digital signal on the same frequency. Electronic circuitry in the satellite must convert that digital signal to a different frequency and re-transmit the signal from the satellite beamed towards earth. The dish antenna mounted on your home has a device called an LNBF. The LNBF is that round white disc mounted on the end of the arm which extends the LNBF out in front of the actual dish antenna.
The signal from the satellite reaches the dish, and gets reflected in a concentrated beam to the LNBF. The LNBF is the actual antenna. The dish just acts like a reflecting magnifying glass and bounces the signal to the LNBF as a concentrated beamed signal. This process increases the strength of the satellite signal entering the LNBF. The LNBF is not just an antenna. It is a box of circuits that does a lot of work. LNBF stands for Low Noise Block Filter.
Basically it receives the digital signal from the satellite on the Ka or Ku band frequency. Then, the circuitry inside the LNBF does another conversion from the Ka or Ku band frequencies, then converts the signals to much lower frequencies in the VHF and UHF range. This is done so a smaller type of coax cable can be used to connect the dish to your receiver box. But we are not done. The set top box in your home must receive the digital signals in the VHF and UHF bands, and convert them again to frequencies that can feed the final signal to your TV set.
Let’s shorten all of that for easier understanding.
- DBS ground station up-links to the satellite on one frequency.
- Satellite converts signal to down-link on another frequency.
- LNBF receives down-link frequency.
- LNBF converts ALL signals to lower frequencies, and sends them to the set top box.
- Set top box converts bit-stream signals to signals for your TV
The original signal has been converted 3 times when it reaches your screen. There is an old rule in transmission of video and audio. Every time you have to convert from one form of signal to another, something must be lost in the translation. And this rule is very true. There is no getting away from it. By the time a DBS signal reaches your TV, it has lost 5 to 10% of it’s original quality. High definition pictures from DBS are still HD, but the sharpness has suffered. This reduces some of the resolution. And that is just the beginning.
Then add the compression.
DBS is a national service provider aimed at the viewers across the country. DBS carries local TV channels just like cable. But DBS must carry local channels for the whole country. There are over 1,700 local TV stations carried on DBS in SD (Standard Definition – 480i). Since the change to HD, DBS now carries most of the local stations in HD also. This brings the total of local stations on DBS to over 3,400.
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